The invention relates to anti-skid systems for motor vehicles, sometimes also called anti-wheel lockup systems. More particularly, the invention relates to anti-skid systems which include wheel motion transducers and processing assemblies which use the signals from these transducers for controlling the hydraulic pressure in one or more of the wheel brakes.
A known anti-skid (anti-wheel lockup) system is described in the German Offenlegungsschrift No. 22 20 441. In the system described there, a plurality of transducers is connected sequentially to a processing channel and a brake pressure control unit engaged by the output signals from the processor channel varies the braking pressure of those wheels which are associated with a particular transducer. In the normal situation, the transducers are connected to the processor channel in a periodic sequence but when anyone of the wheels tends to lock up, the periodic switch-over from one transducer to the other is arrested and instead the transducer signal which indicates a tendency to lock is held connected with the processor channel until the tendency to lock up is no longer present. In the known system, the wheel brakes in which the pressure is jointly varied are the wheels mounted on a single axle.
The known system produces a so-called "select low" control. This type of control design is used for utility vehicles and its application results in increases of the braking distance when the road surface is irregular.